Page 2 of 3 FirstFirst 123 LastLast
  1. Well, to be fair, most of us building our own CNC mills are hobbyists, not engineers. So, the closed rectangular tube is acting as a triangle, in a sense? What if the walls on the smaller set of two square tubes were thicker, say .25" in stead of my 2" x 6", which has 3/16" walls? The weight would be about the same, within a pound or two. I'm leaning toward the singular rectangular tube for sure. Although my hunch is that they would be similar in rigidity due to the fact that the linear rails would ensure that torsion would be applied to both rails evenly, no?
    Thanks for the input magicniner!
    --------------
    Check out my DIY CNC trials and tribulation videos on YouTube: https://youtu.be/SwHb75_GWwM

  2. #12
    Quote Originally Posted by wiremonkey View Post
    What if the walls on the smaller set of two square tubes were thicker
    You get less rigidity and torsional strength for your weight than with one larger box.
    You think that's too expensive? You're not a Model Engineer are you? :D

  3. The Following User Says Thank You to magicniner For This Useful Post:


  4. Here is the Taig in action. I mean, those are some seriously deep cuts! I'm not affiliated with them, I just like the design. https://www.youtube.com/watch?v=_9y-_9SKJ8s
    --------------
    Check out my DIY CNC trials and tribulation videos on YouTube: https://youtu.be/SwHb75_GWwM

  5. #14
    The split tubes have the advantage that the Y axis can be very close to the gantry as it does not need to be offset to accommodate the ballscrew behind it which usually takes up more space than the rail and carriage.

    But it is nowhere near as stiff a shape as a single rectangular gantry. In vertical bending the 2 tubes are only twice as stiff as one of the tubes on its own. But when joined as a single large tube they are 2^3 times stiffer (8 times) for example.
    As mentioned by magicniner there are similar benefits for torsion for similar reasons.

    That is why when you see 2 tube designs with the screw in the middle the builder often plates them together at the back to try and gain some of this advantage back.

    If you go with the single large rectangle then the rails can be spaced out on thick solid bars welded to the section to give the ballscrew clearance. Sure, this puts a moment on the section but you can afford a bit of this loss as you have so much to start with.

    Another variation is to have a tall more slender section vertically and have another horizontal section behind in a reverse L shape. This is popular when used with aluminium extrusions and the ballscrew can sit behind the section driven off a good bracket that often houses the Z stepper too then the rails can be tight against the section again.

    I’d favour the large rectangle as per your blue drawing but the above gives you some options and reasons.
    Building a CNC machine to make a better one since 2010 . . .
    MK1 (1st photo), MK2, MK3, MK4

  6. The Following User Says Thank You to routercnc For This Useful Post:


  7. Thanks for sticking with me routercnc! I plan on putting the lead screw on the face of the X beam, like Wade'o has in his design. In fact, when I can afford it, I intend to switch to a fixed gantry and Y table. Take a peek: https://www.youtube.com/watch?v=herMY_2WowM
    Last edited by wiremonkey; 21-06-2018 at 09:54 PM.
    --------------
    Check out my DIY CNC trials and tribulation videos on YouTube: https://youtu.be/SwHb75_GWwM

  8. OK, so I'm solid on using the 2" x 6" steel tube for the X beam! I have a few more questions for you good folks.

    - 1/4" inch steel plates for the end caps on the beam? Or should I go thicker? 1/2"?

    - 20mm round supported rails and bearings ~$80, or spend the extra dough and get linear rails and bearings ~$240!
    The other factor on the square rails is that I'll have to have the steel beam milled, which will probably cost $200 or more, whereas the supported round rail is far more forgiving when it comes to alignment. The rectangular steel tube has a round crest to it, but it is fairly consistent along the length of the beam. I'm thinking that I can screw the supported round rails right to the beam, maybe a little shim stock if necessary, easy peasy.

    Click image for larger version. 

Name:	round.PNG 
Views:	13 
Size:	182.5 KB 
ID:	24471 VS. Click image for larger version. 

Name:	Capture.PNG 
Views:	13 
Size:	94.9 KB 
ID:	24472

    I'd love to hear your thoughts on these two issues.
    Cheers!
    Last edited by wiremonkey; 24-06-2018 at 12:48 AM.
    --------------
    Check out my DIY CNC trials and tribulation videos on YouTube: https://youtu.be/SwHb75_GWwM

  9. #17
    Doddy's Avatar
    Lives in Preston, United Kingdom. Last Activity: 5 Hours Ago Has been a member for 4-5 years. Has a total post count of 299. Received thanks 34 times, giving thanks to others 10 times.
    Linear rail, and epoxy?

  10. The Following User Says Thank You to Doddy For This Useful Post:


  11. #18
    I'd love to hear your thoughts on these two issues.
    Cheers!
    Yes what Doddy said
    ..Clive
    The more you know, The better you know, How little you know

  12. The Following User Says Thank You to Clive S For This Useful Post:


  13. #19
    Supported rail will be better than the wheels you have now and my previous machine ran on those for a few years. But there can be some maintenance such as sometimes the bearing coming loose in the housing plus there was some wear on my set that I noticed when I took them apart and was the likely cause of it getting worse for chatter.
    So if you stay in this hobby you will get linear profile rails in the end.
    As for the gantry sides - looks like they are the drop down style to raise the gantry. So they need to be quite thick. If they are aluminium then they should ideally be 20mm. But if they are steel they can be thinner. Steel is 3 times stiffer than aluminium, just in terms of material properties, but then when you go thinner you quickly loose out due to geometry (which is independent of material) so . . . go for 12.5 mm over 6.35 mm.
    Better still if doing a really good upgrade raise the bed sides so the gantry doesn’t have to drop down and you will gain much more than trying to get stiffness back in the side plates.
    Building a CNC machine to make a better one since 2010 . . .
    MK1 (1st photo), MK2, MK3, MK4

  14. The Following User Says Thank You to routercnc For This Useful Post:


  15. Linear rails are far superior to round supported rails.
    Gerry
    ______________________________________________
    UCCNC 2017 Screenset

    Mach3 2010 Screenset

    JointCAM - CAM for Woodworking Joints

  16. The Following 2 Users Say Thank You to Ger21 For This Useful Post:


Page 2 of 3 FirstFirst 123 LastLast

Similar Threads

  1. Shallow channel/Contour
    By dfox1787 in forum Fusion 360
    Replies: 6
    Last Post: 08-05-2018, 10:49 AM
  2. Beam choice
    By idegraaf in forum Gantry/Router Machines & Building
    Replies: 6
    Last Post: 22-03-2018, 06:38 PM
  3. BUILD LOG: New build - Steel - 3 Axis initially then conversion to 4 axis.
    By Slixxor in forum DIY Router Build Logs
    Replies: 44
    Last Post: 29-12-2016, 01:57 AM
  4. DeskProto 3D cam software, forum support added!
    By Lee Roberts in forum DeskProto
    Replies: 0
    Last Post: 27-01-2014, 02:21 PM
  5. He's added a fourth axis
    By GeorgeD in forum Gantry/Router Machines & Building
    Replies: 39
    Last Post: 01-08-2010, 07:33 PM

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •